Computing devices that allow a user to provide finger touch input and also allow a user to provide input with an active stylus are known. Many of these computing devices are designed to be self powered and handheld, e.g. laptops, trackpads, MP3 players and smart-phones. Others may be designed to be desktop devices. A digitizer system for detecting finger touch input and stylus input may be integrated on a touch screen to form a touch sensitive screen and may also be integrated on a trackpad.
A grid based capacitive sensor is one type of digitizer sensor that may be integrated with an electronic display of the computing device to form the touch sensitive screen and may also be used on a trackpad. Grid based capacitive sensors typically track free style input provided with an object such as a finger or a conductive object with a mutual capacitive or self-capacitive detection method. During both mutual capacitive detection and self-capacitive detection, a circuit associated with the digitizer sensor transmits a drive signal on one or more grid lines of the digitizer sensor and detects a capacitive load in response to the drive signal. The circuit may also be configured to detect signals emitted by a stylus and track position of the stylus. The digitizer sensor together with the associated circuit is a digitizer system. Coordinates of the tracked object (stylus and finger) may be reported to the computing device and interpreted as user commands or user inputs for commands.